The invention relates to in-well mounting and positioning devices, in particular to an in-well mounting and positioning device for crude oil viscosity reduction equipment. The in-well mounting and positioning device comprises a mounting sleeve, an upper sliding ring, supporting rods I, supporting rods II, pulleys I, a middle sliding ring, supporting rods III, supporting rods IV, pulleys II and anadjusting screw rod, wherein the upper sliding ring is connected to the upper end of the mounting sleeve in a sliding mode, the middle sliding ring is connected to the middle end of the mounting sleeve in a sliding mode, the supporting rods I and/or the supporting rods II are elastic rods, and the supporting rods III and/or the supporting rods IV are elastic rods; and the middle end of the middlesliding ring is provided with an arc-shaped rod I, an arc-shaped rod II and an inner-pipe positioning piece, one end of the arc-shaped rod I is hinged to one end of the arc-shaped rod II through an articulated shaft III, the other end of the arc-shaped rod I and the other end of the arc-shaped rod II both connected to the mounting sleeve in a sliding mod, and the inner-pipe positioning piece is rotationally connected to the articulated shaft III. According to the in-well mounting and positioning device, centering and fixing can be carried out in the well, the structure is compact, and the fixation is firm.